1. Field of the Invention
The present invention relates generally to impact printing mechanisms used in printing devices such as typewriters and printers and more particularly to a print hammer used in such a mechanism which dampens acoustic noise generated during operation of a printing mechanism.
2. Description of the Prior Art
Both typewriters and printers utilizing impact printing mechanisms often generate high levels of acoustic noise. There have been various solutions proposed to lower the noise generated by such printing mechanisms. It has, for example, been the practice in the typewriter and printer art to reduce noise by the use of platens having a reduced hardness. This solution has, however, been found to also reduce the print quality. Another practice has been to reduce the required impact velocity by increasing the effective or apparent mass of the hammer or anvil.
Increasing the effective mass of the print hammer allows reduction of impact velocity to attain equivalent print quality. A weighted hammer, however, like conventional hammers, does contribute to coupling the acoustic noise generated during impact, back through the print drive assembly.
Other solutions to the foregoing problem include noise dampening structures and materials for use in impact printing mechanisms. For example, U.S. Pat. No. 4,318,452 discloses a dampening material interposed between a support beam and a metal strip. The strip receives the impact of typewriter typebars and other noise inducing mechanical force elements of printing. The noise emanating from the impacts is dampened as it travels through the material. Also, U.S. Pat. No. 1,615,976 discloses a typebar which includes a shock absorbing means. Shock absorbing material is disposed between a "U" shaped member and the typebar whereby the shock impact energy is absorbed when movement of the typebar is arrested at impact during the print cycle. In addition, U.S. Pat. No. 2,157,607 discloses a typebar abutment which includes an arcuate cage and a plurality of filler plates tightly filling the cage. The plates are spaced apart by air films and function to interrupt and dampen sound waves generated when the typebars strike the abutment to thereby reduce the impact noise.